Phosphate compounds such as sodium polyphosphate are inhibitors used to tie up forming ions. What is another name for these inhibitors?

• A. Coagulants
• B. Sequestering agents
• C. Scavengers
• D. Buffering agents

Answer: (B)

Phosphate compounds like sodium polyphosphate act as sequestering agents in water treatment. They bind with metal forming ions such as calcium, magnesium, iron, and manganese to form soluble complexes, preventing these ions from precipitating as scale or causing staining. This keeps minerals in solution and helps control hardness and corrosion. Coagulants are used to remove suspended particles, buffering agents stabilize pH, and while scavengers remove certain contaminants, they don’t describe the function of tying up metal ions in solution. So the term that best fits is sequestering agents.